IL-10 deficiency promotes increased Borrelia burgdorferi clearance predominantly through enhanced innate immune responses

A comprehensive genetic map of cytokine responses in Lyme borreliosis

The incidence of Lyme borreliosis has risen, accompanied by persistent symptoms. The innate immune system and related cytokines are crucial in the host response and symptom development. We characterized cytokine production capacity before and after antibiotic treatment in 1,060 Lyme borreliosis patients. We observed a negative correlation between antibody production and IL-10 responses, as well as increased IL-1Ra responses in patients with disseminated disease. Genome-wide mapping the cytokine production allowed us to identify 34 cytokine quantitative trait loci (cQTLs), with 31 novel ones. We pinpointed the causal variant at the TLR1-6-10 locus and validated the regulation of IL-1Ra responses at transcritpome level using an independent cohort. We found that cQTLs contribute to Lyme borreliosis susceptibility and are relevant to other immune-mediated diseases. Our findings improve the understanding of cytokine responses in Lyme borreliosis and provide a genetic map of immune function as an expanded resource.

Borrelia burgdorferi initiates early transcriptional re-programming in macrophages that supports long-term suppression of inflammation

Borrelia burgdorferi (Bb), the causative agent of Lyme disease, establishes a long-term infection and leads to disease manifestations that are the result of host immune responses to the pathogen. Inflammatory manifestations resolve spontaneously despite continued bacterial presence, suggesting inflammatory cells become less responsive over time. This is mimicked by in vitro repeated stimulations, resulting in tolerance, a phenotypic subset of innate immune memory. We performed comparative transcriptional analysis of macrophages in acute and memory states and identified sets of Tolerized, Hyper-Induced, Secondary-Induced and Hyper-Suppressed genes resulting from memory induction, revealing previously unexplored networks of genes affected by cellular re-programming. Tolerized gene families included inflammatory mediators and interferon related genes as would be predicted by the attenuation of inflammation over time. To better understand how cells mediate inflammatory hypo-responsiveness, we focused on genes that could mediate maintenance of suppression, such as Hyper-Induced genes which are up-regulated in memory states. These genes were notably enriched in stress pathways regulated by anti-inflammatory modulators. We examined one of the most highly expressed negative regulators of immune pathways during primary stimulation, Aconitate decarboxylase 1 (Acod1), and tested its effects during in vivo infection with Bb. As predicted by our in vitro model, we show its inflammation-suppressive downstream effects are sustained during in vivo long-term infection with Bb, with a specific role in Lyme carditis.

Determinants of persistent symptoms after treatment for Lyme borreliosis: a prospective observational cohort study

BACKGROUND

Patients treated for Lyme borreliosis (LB) frequently report persistent symptoms. Little is known about risk factors and etiology.

METHODS

In a prospective observational cohort study with a follow-up of one year, we assessed a range of microbiological, immunological, genetic, clinical, functional, epidemiological, psychosocial and cognitive-behavioral variables as determinants of persistent symptoms after treatment for LB. Between 2015 and 2018 we included 1135 physician-confirmed LB patients at initiation of antibiotic therapy, through clinical LB centers and online self-registration. Two reference cohorts of individuals without LB (n = 4000 and n = 2405) served as a control. Prediction analyses and association studies were used to identify determinants, as collected from online questionnaires (three-monthly) and laboratory tests (twice).

FINDINGS

Main predictors of persistent symptoms were baseline poorer physical and social functioning, higher depression and anxiety scores, more negative illness perceptions, comorbidity, as well as fatigue, cognitive impairment, and pain in 295 patients with persistent symptoms. The primary prediction model correctly indicated persistent symptoms in 71.0% of predictions (AUC 0.79). In patients with symptoms at baseline, cognitive-behavioral responses to symptoms predicted symptom persistence. Of various microbiological, immunological and genetic factors, only lower IL-10 concentrations in ex vivo stimulation experiments were associated with persistent symptoms. Clinical LB characteristics did not contribute to the prediction of persistent symptoms.

INTERPRETATION

Determinants of persistent symptoms after LB were mainly generic, including baseline functioning, symptoms and cognitive-behavioral responses. A potential role of host immune responses remains to be investigated.

FUNDING

Netherlands Organisation for Health Research and Development (ZonMw); the Dutch Ministry of Health, Welfare and Sport (VWS).

The Brilliance of Borrelia: Mechanisms of Host Immune Evasion by Lyme Disease-Causing Spirochetes

Lyme disease (LD) has become the most common vector-borne illness in the northern hemisphere. The causative agent, Borrelia burgdorferi sensu lato, is capable of establishing a persistent infection within the host. This is despite the activation of both the innate and adaptive immune responses. B. burgdorferi utilizes several immune evasion tactics ranging from the regulation of surface proteins, tick saliva, antimicrobial peptide resistance, and the disabling of the germinal center. This review aims to cover the various methods by which B. burgdorferi evades detection and destruction by the host immune response, examining both the innate and adaptive responses. By understanding the methods employed by B. burgdorferi to evade the host immune response, we gain a deeper knowledge of B. burgdorferi pathogenesis and Lyme disease, and gain insight into how to create novel, effective treatments.

Elevated inflammatory responses and targeted therapeutic intervention in a preclinical mouse model of ataxia-telangiectasia lung disease

Ataxia-telangiectasia (A-T) is an autosomal recessive, multisystem disorder characterized by cerebellar degeneration, cancer predisposition, and immune system defects. A major cause of mortality in A-T patients is severe pulmonary disease; however, the underlying causes of the lung complications are poorly understood, and there are currently no curative therapeutic interventions. In this study, we examined the lung phenotypes caused by ATM-deficient immune cells using a mouse model of A-T pulmonary disease. In response to acute lung injury, ATM-deficiency causes decreased survival, reduced blood oxygen saturation, elevated neutrophil recruitment, exaggerated and prolonged inflammatory responses and excessive lung injury compared to controls. We found that ATM null bone marrow adoptively transferred to WT recipients induces similar phenotypes that culminate in impaired lung function. Moreover, we demonstrated that activated ATM-deficient macrophages exhibit significantly elevated production of harmful reactive oxygen and nitrogen species and pro-inflammatory cytokines. These findings indicate that ATM-deficient immune cells play major roles in causing the lung pathologies in A-T. Based on these results, we examined the impact of inhibiting the aberrant inflammatory responses caused by ATM-deficiency with reparixin, a CXCR1/CXCR2 chemokine receptor antagonist. We demonstrated that reparixin treatment reduces neutrophil recruitment, edema and tissue damage in ATM mutant lungs. Thus, our findings indicate that targeted inhibition of CXCR1/CXCR2 attenuates pulmonary phenotypes caused by ATM-deficiency and suggest that this treatment approach represents a viable therapeutic strategy for A-T lung disease.

Molecular Interactions During Borrelia burgdorferi Migration from the Vector to the Mammalian Nervous System

Lyme disease (LD) is an infectious disease caused by the spirochetes of genus borrelia, which are transmitted by the ticks of the genus ixodes. LD is transmitted by the spirochete B. burgdorferi sensu lato. Once in contact with the host through a tick bite, the pathogen comes into contact with the host defense, and must escape this machinery to establish LD, thus using a large number of mechanisms involving the vector of the pathogen, the pathogen itself and also the host. The initial diagnosis of the disease can be made based on the clinical symptoms of LD and the disease can be treated and cured with antibiotics if the diagnosis is made early in the beginning of the disease. Contrariwise, if LD is left untreated, the pathogen disseminates throughout the tissues and organs of the body, where it establishes different types of disease manifestations. In the nervous system, the inflammation caused by B. burgdorferi is known as Lyme neuroborreliosis (LNB). LNB is one of the principal manifestations of LD. In this review, we systematically describe the different molecular interactions among B. burgdorferi, the vector (tick) and the mammalian host.

Systemic immune responses in patients with early localized or early disseminated Borrelia afzelii lyme borreliosis

Introduction

The role of host immune responses in the pathogenesis of borrelial dissemination in early Lyme borreliosis (LB) in the form of multiple erythema migrans (MEM) or LB‐associated symptoms is incompletely understood.

Methods

In this study, fifteen cytokine or chemokine levels, representative of innate, Th1, and Th17 immune responses, were assessed using a bead‐based Luminex multiplex assay in acute sera from 76 adult patients with skin culture‐positive Borrelia afzelii solitary erythema migrans (SEM) and 58 patients with MEM at a single‐center university hospital. Differences between the groups were tested by modeling each cytokine or chemokine concentration by means of left‐censored regression using the classic Tobit model.

Results

Mean serum cytokine or chemokine levels were low. When taking into account the proportion of patients with cytokine or chemokine concentrations below the lowest detectable limit, only levels of CXCL10 (p = .03) and CCL19 (p = .02), representatives of the Th1 immune response, differed between patients with SEM and those with MEM; however, the differences did not reach statistical significance when adjusted for multiple comparisons. In addition, we did not find differences in systemic inflammatory responses when comparing patients with and those without LB‐associated constitutional symptoms.

Conclusion

No significant differences in systemic immune responses represented by selected cytokines or chemokines in serum samples of patients with EM infected with B. afzelii suggest that systemic mediators are not pivotal in the pathogenesis of dissemination of early infection in the form of MEM or LB‐associated symptoms. Localized immune responses in the skin or other pathogenetic mechanisms may be more important in this regard.

Regulatory T Cells Contribute to Resistance against Lyme Arthritis

The symptoms of Lyme disease are caused by inflammation induced by species of the Borrelia burgdorferi sensu lato complex. The various presentations of Lyme disease in the population suggest that differences exist in the intensity and regulation of the host response to the spirochete. Previous work has described correlations between the presence of regulatory T cells and recovery from Lyme arthritis. However, the effects of Foxp3-expressing CD4⁺ T cells existing prior to, and during, B. burgdorferi infection have not been well characterized. Here, we used C57BL/6 "depletion of regulatory T cell" mice to assess the effects these cells have on the arthritis-resistant phenotype characteristic of this mouse strain. We showed that depletion of regulatory T cells prior to infection with B. burgdorferi resulted in sustained swelling, as well as histopathological changes, of the tibiotarsal joints that were not observed in infected control mice. Additionally, in vitro stimulation of splenocytes from these regulatory T cell-depleted mice resulted in increases in gamma interferon and interleukin-17 production and decreases in interleukin-10 production that were not evident among splenocytes of infected mice in which Treg cells were not depleted. Depletion of regulatory T cells at various times after infection also induced rapid joint swelling. Collectively, these findings provide evidence that regulatory T cells existing at the time of, and possibly after, B. burgdorferi infection may play an important role in limiting the development of arthritis.

Skin Interface, a Key Player for Borrelia Multiplication and Persistence in Lyme Borreliosis

The skin plays a key role in vector-borne diseases because it is the site where the arthropod coinoculates pathogens and its saliva. Lyme borreliosis, particularly well investigated in this context, is a multisystemic infectious disease caused by Borrelia burgdorferi sensu lato and transmitted by the hard tick Ixodes. Numerous in vitro studies were conducted to better understand the role of specific skin cells and tick saliva in host defense, vector feeding, and pathogen transmission. The skin was also evidenced in various animal models as the site of bacterial multiplication and persistence. We present the achievements in this field as well as the gaps that impede comprehensive knowledge of the disease pathophysiology and the development of efficient diagnostic tools and vaccines in humans.

Ablating astrocyte insulin receptors leads to delayed puberty and hypogonadism in mice

Insulin resistance and obesity are associated with reduced gonadotropin-releasing hormone (GnRH) release and infertility. Mice that lack insulin receptors (IRs) throughout development in both neuronal and non-neuronal brain cells are known to exhibit subfertility due to hypogonadotropic hypogonadism. However, attempts to recapitulate this phenotype by targeting specific neurons have failed. To determine whether astrocytic insulin sensing plays a role in the regulation of fertility, we generated mice lacking IRs in astrocytes (astrocyte-specific insulin receptor deletion [IRKOGFAP] mice). IRKOGFAP males and females showed a delay in balanopreputial separation or vaginal opening and first estrous, respectively. In adulthood, IRKOGFAP female mice also exhibited longer, irregular estrus cycles, decreased pregnancy rates, and reduced litter sizes. IRKOGFAP mice show normal sexual behavior but hypothalamic-pituitary-gonadotropin (HPG) axis dysregulation, likely explaining their low fecundity. Histological examination of testes and ovaries showed impaired spermatogenesis and ovarian follicle maturation. Finally, reduced prostaglandin E synthase 2 (PGES2) levels were found in astrocytes isolated from these mice, suggesting a mechanism for low GnRH/luteinizing hormone (LH) secretion. These findings demonstrate that insulin sensing by astrocytes is indispensable for the function of the reproductive axis. Additional work is needed to elucidate the role of astrocytes in the maturation of hypothalamic reproductive circuits.

The Classical Complement Pathway Is Required to Control Borrelia burgdorferi Levels During Experimental Infection

Activation of the classical complement pathway occurs to varying degrees within strains of the Borrelia burgdorferi sensu lato complex, which contain a group of pathogenic spirochetes that cause tick-borne Lyme borreliosis, including the agent of Lyme disease in the United States, B. burgdorferi. Despite this information, details related to the control of B. burgdorferi by the classical pathway are not clear. To address this question, we infected C1qα^-/- mice, which cannot assemble the C1 complex and thus fail to activate the classical pathway, with B. burgdorferi sensu stricto strain B31. Using bioluminescent in vivo imaging, we found that C1qα^-/- mice harbored more B. burgdorferi following 10 days of infection relative to their isogenic C57BL/6 parent. Quantitative PCR (qPCR) demonstrated that C1qα^-/- mice harbored significantly more B. burgdorferi than parent mice did within lymph nodes, skin, heart, and joints. The increased B. burgdorferi load in C1qα^-/- mice was observed at 21 and 28 days of infection, consistent with the classical pathway promoting complement-dependent, antibody-mediated killing following the development of a B. burgdorferi-specific humoral immune response. In addition, circulating borrelial-specific IgM was higher in C1qα^-/- mice relative to their parent mouse strain and did not decrease at 21 and 28 days post-infection, indicating that IgG class switching was delayed in C1qα^-/- mice. At day 28, both Borrelia-specific IgG1 and IgG3 levels were higher in infected C1qα^-/- mice, but that these antibodies were not sufficient to control borrelial infection in the absence of the classical pathway. Furthermore, the lack of C1q also altered the balance of the Th1/Th2 response, as both circulating Th1 (MIP-1α, IL-2, IL-12, and TNFα), Th2 (IL-4, IL-10, and MCP-1), and Th17 (IL-17) cytokines were elevated in infected C1qα^-/- mice. These data imply that C1q and the classical pathway play important roles in controlling borrelial infection via antibody and complement-dependent killing, as well as altering both antibody maturation processes and the T cell response following exposure to infectious B. burgdorferi.

Induction of Interleukin 10 by Borrelia burgdorferi Is Regulated by the Action of CD14-Dependent p38 Mitogen-Activated Protein Kinase and cAMP-Mediated Chromatin Remodeling

Host genotype influences the severity of murine Lyme borreliosis, caused by the spirochetal bacterium Borrelia burgdorferi C57BL/6 (B6) mice develop mild Lyme arthritis, whereas C3H/HeN (C3H) mice develop severe Lyme arthritis. Differential expression of interleukin 10 (IL-10) has long been associated with mouse strain differences in Lyme pathogenesis; however, the underlying mechanism(s) of this genotype-specific IL-10 regulation remained elusive. Herein we reveal a cAMP-mediated mechanism of IL-10 regulation in B6 macrophages that is substantially diminished in C3H macrophages. Under cAMP and CD14-p38 mitogen-activated protein kinase (MAPK) signaling, B6 macrophages stimulated with B. burgdorferi produce increased amounts of IL-10 and decreased levels of arthritogenic cytokines, including tumor necrosis factor (TNF). cAMP relaxes chromatin, while p38 increases binding of the transcription factors signal transducer and activator of transcription 3 (STAT3) and specific protein 1 (SP1) to the IL-10 promoter, leading to increased IL-10 production in B6 bone marrow-derived monocytes (BMDMs). Conversely, macrophages derived from arthritis-susceptible C3H mice possess significantly less endogenous cAMP, produce less IL-10, and thus are ill equipped to mitigate the damaging consequences of B. burgdorferi-induced TNF. Intriguingly, an altered balance between anti-inflammatory and proinflammatory cytokines and CD14-dependent regulatory mechanisms also is operative in primary human peripheral blood-derived monocytes, providing potential insight into the clinical spectrum of human Lyme disease. In line with this notion, we have demonstrated that cAMP-enhancing drugs increase IL-10 production in myeloid cells, thus curtailing inflammation associated with murine Lyme borreliosis. Discovery of novel treatments or repurposing of FDA-approved cAMP-modulating medications may be a promising avenue for treatment of patients with adverse clinical outcomes, including certain post-Lyme complications, in whom dysregulated immune responses may play a role.

Il-10 deficient mice express IFN-γ mRNA and clear Leptospira interrogans from their kidneys more rapidly than normal C57BL/6 mice

Leptospira interrogans (L. interrogans), the causative agent of leptospirosis, is a widespread zoonotic spirochete that lives a dual lifestyle. L. interrogans infects mice, rats, and wildlife in a persistent and asymptomatic fashion, while also causing productive and acute infections in other mammals such as humans and hamsters. Infections in humans can be fatal, accompanied by a cytokine storm and shock-like symptoms. Production of IL-10 has been noted in both rodent and human infections which has led a number of investigators to hypothesize that IL-10 plays a role in the pathogenesis of this disease. To test this hypothesis we have compared bacteremia and the cytokine response of normal and IL-10 deficient C57Bl/6 mice following ip infection with L. interrogans. In normal mice bacterial 16s mRNA was detected in both lung and kidney tissues within a day after infection. Levels of 16s mRNA then dropped in both organs with complete elimination from the lung by day 3 but persistence in the kidney for 7days after infection. In contrast, in IL-10 deficient mice, the organism was eliminated more rapidly from the kidney. We found that infection of both control and IL-10 deficient mice produced similar levels of a number of pro-inflammatory cytokine mRNAs. On the other hand, IFN-γ mRNA was only induced in IL-10 deficient mice. These results support the hypothesis that L. interrogans ability to induce IL-10, which in turn prevents production of IFN-γ and inhibits T cell immunity, may contribute to the persistent growth of this microorganism in the murine kidney.

Lyme borreliosis

Lyme borreliosis is a tick-borne disease that predominantly occurs in temperate regions of the northern hemisphere and is primarily caused by the bacterium Borrelia burgdorferi in North America and Borrelia afzelii or Borrelia garinii in Europe and Asia. Infection usually begins with an expanding skin lesion, known as erythema migrans (referred to as stage 1), which, if untreated, can be followed by early disseminated infection, particularly neurological abnormalities (stage 2), and by late infection, especially arthritis in North America or acrodermatitis chronica atrophicans in Europe (stage 3). However, the disease can present with any of these manifestations. During infection, the bacteria migrate through the host tissues, adhere to certain cells and can evade immune clearance. Yet, these organisms are eventually killed by both innate and adaptive immune responses and most inflammatory manifestations of the infection resolve. Except for patients with erythema migrans, Lyme borreliosis is diagnosed based on a characteristic clinical constellation of signs and symptoms with serological confirmation of infection. All manifestations of the infection can usually be treated with appropriate antibiotic regimens, but the disease can be followed by post-infectious sequelae in some patients. Prevention of Lyme borreliosis primarily involves the avoidance of tick bites by personal protective measures.

CD4+ cell-derived interleukin-17 in a model of dysregulated, Borrelia-induced arthritis

Lyme borreliosis, which is caused in the United States by the spirochete Borrelia burgdorferi, may manifest as different arrays of signs, symptoms and severities between infected individuals. Recent studies have indicated that particularly severe forms of Lyme borreliosis in humans are associated with an increased Th17 response. Here, we hypothesized that a murine model combining the dysregulated immune response of an environment lacking interleukin-10 (IL-10) with a robust T-cell-driven inflammatory response would reflect arthritis associated with the production of IL-17 by CD4+ cells. We demonstrate that IL-10 regulates the production of IL-17 by Borrelia-primed CD4+ cells early after interaction with Lyme spirochetes in vitro and that infection of Borrelia-primed mice with B. burgdorferi leads to significant production of IL-17 that contributes to the development of severe arthritis. These results extend our previous findings by demonstrating that a dysregulated adaptive immune response to Lyme spirochetes can contribute to severe, Th17-associated arthritis. These findings may lead to therapeutic measures for individuals with particularly severe symptoms of Lyme borreliosis.

Pleomorphic forms of Borrelia burgdorferi induce distinct immune responses

Borrelia burgdorferi is the causative agent of tick-borne Lyme disease. As a response to environmental stress B. burgdorferi can change its morphology to a round body form. The role of B. burgdorferi pleomorphic forms in Lyme disease pathogenesis has long been debated and unclear. Here, we demonstrated that round bodies were processed differently in differentiated macrophages, consequently inducing distinct immune responses compared to spirochetes in vitro. Colocalization analysis indicated that the F-actin participates in internalization of both forms. However, round bodies end up less in macrophage lysosomes than spirochetes suggesting that there are differences in processing of these forms in phagocytic cells. Furthermore, round bodies stimulated distinct cytokine and chemokine production in these cells. We confirmed that spirochetes and round bodies present different protein profiles and antigenicity. In a Western blot analysis Lyme disease patients had more intense responses to round bodies when compared to spirochetes. These results suggest that round bodies have a role in Lyme disease pathogenesis.

Antagonistic Interplay between MicroRNA-155 and IL-10 during Lyme Carditis and Arthritis

MicroRNA-155 has been shown to play a role in immune activation and inflammation, and is suppressed by IL-10, an important anti-inflammatory cytokine. The established involvement of IL-10 in the murine model of Borrelia burgdorferi-induced Lyme arthritis and carditis allowed us to assess the interplay between IL-10 and miR-155 in vivo. As reported previously, Mir155 was highly upregulated in joints from infected severely arthritic B6 Il10^-/- mice, but not in mildly arthritic B6 mice. In infected hearts, Mir155 was upregulated in both strains, suggesting a role of miR-155 in Lyme carditis. Using B. burgdorferi-infected B6, Mir155^-/-, Il10^-/-, and Mir155^-/- Il10^-/- double-knockout (DKO) mice, we found that anti-inflammatory IL-10 and pro-inflammatory miR-155 have opposite and somewhat compensatory effects on myeloid cell activity, cytokine production, and antibody response. Both IL-10 and miR-155 were required for suppression of Lyme carditis. Infected Mir155^-/- mice developed moderate/severe carditis, had higher B. burgdorferi numbers, and had reduced Th1 cytokine expression in hearts. In contrast, while Il10^-/- and DKO mice also developed severe carditis, hearts had reduced bacterial numbers and elevated Th1 and innate cytokine expression. Surprisingly, miR-155 had little effect on Lyme arthritis. These results show that antagonistic interplay between IL-10 and miR-155 is required to balance host defense and immune activation in vivo, and this balance is particularly important for suppression of Lyme carditis. These results also highlight tissue-specific differences in Lyme arthritis and carditis pathogenesis, and reveal the importance of IL-10-mediated regulation of miR-155 in maintaining healthy immunity.

BB0744 Affects Tissue Tropism and Spatial Distribution of Borrelia burgdorferi

Borrelia burgdorferi, the etiologic agent of Lyme disease, produces a variety of proteins that promote survival and colonization in both the Ixodes species vector and various mammalian hosts. We initially identified BB0744 (also known as p83/100) by screening for B. burgdorferi strain B31 proteins that bind to α1β1 integrin and hypothesized that, given the presence of a signal peptide, BB0744 may be a surface-exposed protein. In contrast to this expectation, localization studies suggested that BB0744 resides in the periplasm. Despite its subsurface location, we were interested in testing whether BB0744 is required for borrelial pathogenesis. To this end, a bb0744 deletion was isolated in a B. burgdorferi strain B31 infectious background, complemented, and queried for the role of BB0744 following experimental infection. A combination of bioluminescent imaging, cultivation of infected tissues, and quantitative PCR (qPCR) demonstrated that Δbb0744 mutant B. burgdorferi bacteria were attenuated in the ability to colonize heart tissue, as well as skin locations distal to the site of infection. Furthermore, qPCR indicated a significantly reduced spirochetal load in distal skin and joint tissue infected with Δbb0744 mutant B. burgdorferi. Complementation with bb0744 restored infectivity, indicating that the defect seen in Δbb0744 mutant B. burgdorferi was due to the loss of BB0744. Taken together, these results suggest that BB0744 is necessary for tissue tropism, particularly in heart tissue, alters the ability of B. burgdorferi to disseminate efficiently, or both. Additional studies are warranted to address the mechanism employed by BB0744 that alters the pathogenic potential of B. burgdorferi.

Motor rotation is essential for the formation of the periplasmic flagellar ribbon, cellular morphology, and Borrelia burgdorferi persistence within Ixodes scapularis tick and murine hosts

Borrelia burgdorferi must migrate within and between its arthropod and mammalian hosts in order to complete its natural enzootic cycle. During tick feeding, the spirochete transmits from the tick to the host dermis, eventually colonizing and persisting within multiple, distant tissues. This dissemination modality suggests that flagellar motor rotation and, by extension, motility are crucial for infection. We recently reported that a nonmotile flaB mutant that lacks periplasmic flagella is rod shaped and unable to infect mice by needle or tick bite. However, those studies could not differentiate whether motor rotation or merely the possession of the periplasmic flagella was crucial for cellular morphology and host persistence. Here, we constructed and characterized a motB mutant that is nonmotile but retains its periplasmic flagella. Even though ΔmotB bacteria assembled flagella, part of the mutant cell is rod shaped. Cryoelectron tomography revealed that the flagellar ribbons are distorted in the mutant cells, indicating that motor rotation is essential for spirochetal flat-wave morphology. The ΔmotB cells are unable to infect mice, survive in the vector, or migrate out of the tick. Coinfection studies determined that the presence of these nonmotile ΔmotB cells has no effect on the clearance of wild-type spirochetes during murine infection and vice versa. Together, our data demonstrate that while flagellar motor rotation is necessary for spirochetal morphology and motility, the periplasmic flagella display no additional properties related to immune clearance and persistence within relevant hosts.

Early cytokine release in response to live Borrelia burgdorferi Sensu Lato Spirochetes is largely complement independent

Aim

Here we investigated the role of complement activation in phagocytosis and the release of cytokines and chemokines in response to two clinical isolates: Borrelia afzelii K78, which is resistant to complement-mediated lysis, and Borrelia garinii LU59, which is complement-sensitive.

Methods

Borrelia spirochetes were incubated in hirudin plasma, or hirudin-anticoagulated whole blood. Complement activation was measured as the generation of C3a and sC5b-9. Binding of the complement components C3, factor H, C4, and C4BP to the bacterial surfaces was analyzed. The importance of complement activation on phagocytosis, and on the release of cytokines and chemokines, was investigated using inhibitors acting at different levels of the complement cascade.

Results

1) Borrelia garinii LU59 induced significantly higher complement activation than did Borrelia afzelii K78. 2) Borrelia afzelii K78 recruited higher amounts of factor H resulting in significantly lower C3 binding. 3) Both Borrelia strains were efficiently phagocytized by granulocytes and monocytes, with substantial inhibition by complement blockade at the levels of C3 and C5. 4) The release of the pro-inflammatory cytokines and chemokines IL-1β, IL-6, TNF, CCL20, and CXCL8, together with the anti-inflammatory IL-10, were increased the most (by>10-fold after exposure to Borrelia). 5) Both strains induced a similar release of cytokines and chemokines, which in contrast to the phagocytosis, was almost totally unaffected by complement blockade.

Conclusions

Our results show that complement activation plays an important role in the process of phagocytosis but not in the subsequent cytokine release in response to live Borrelia spirochetes.

Delineating the importance of serum opsonins and the bacterial capsule in affecting the uptake and killing of Burkholderia pseudomallei by murine neutrophils and macrophages

Infection of susceptible hosts by the encapsulated Gram-negative bacterium Burkholderia pseudomallei (Bp) causes melioidosis, with septic patients attaining mortality rates ≥ 40%. Due to its high infectivity through inhalation and limited effective therapies, Bp is considered a potential bioweapon. Thus, there is great interest in identifying immune effectors that effectively kill Bp. Our goal is to compare the relative abilities of murine macrophages and neutrophils to clear Bp, as well as determine the importance of serum opsonins and bacterial capsule. Our findings indicate that murine macrophages and neutrophils are inherently unable to clear either unopsonized Bp or the relatively-avirulent acapsular bacterium B. thailandensis (Bt). Opsonization of Bp and Bt with complement or pathogen-specific antibodies increases macrophage-uptake, but does not promote clearance, although antibody-binding enhances complement deposition. In contrast, complement opsonization of Bp and Bt causes enhanced uptake and killing by neutrophils, which is linked with rapid ROS induction against bacteria exhibiting a threshold level of complement deposition. Addition of bacteria-specific antibodies enhances complement deposition, but antibody-binding alone cannot elicit neutrophil clearance. Bp capsule provides some resistance to complement deposition, but is not anti-phagocytic or protective against reactive oxygen species (ROS)-killing. Macrophages were observed to efficiently clear Bp only after pre-activation with IFNγ, which is independent of serum- and/or antibody-opsonization. These studies indicate that antibody-enhanced complement activation is sufficient for neutrophil-clearance of Bp, whereas macrophages are ineffective at clearing serum-opsonized Bp unless pre-activated with IFNγ. This suggests that effective immune therapies would need to elicit both antibodies and Th1-adaptive responses for successful prevention/eradication of melioidosis.

MicroRNA-146a provides feedback regulation of lyme arthritis but not carditis during infection with Borrelia burgdorferi

MicroRNAs have been shown to be important regulators of inflammatory and immune responses and are implicated in several immune disorders including systemic lupus erythematosus and rheumatoid arthritis, but their role in Lyme borreliosis remains unknown. We performed a microarray screen for expression of miRNAs in joint tissue from three mouse strains infected with Borrelia burgdorferi. This screen identified upregulation of miR-146a, a key negative regulator of NF-κB signaling, in all three strains, suggesting it plays an important role in the in vivo response to B. burgdorferi. Infection of B6 miR-146a-/- mice with B. burgdorferi revealed a critical nonredundant role of miR-146a in modulating Lyme arthritis without compromising host immune response or heart inflammation. The impact of miR-146a was specifically localized to the joint, and did not impact lesion development or inflammation in the heart. Furthermore, B6 miR-146a-/- mice had elevated levels of NF-κB-regulated products in joint tissue and serum late in infection. Flow cytometry analysis of various lineages isolated from infected joint tissue of mice showed that myeloid cell infiltration was significantly greater in B6 miR-146a-/- mice, compared to B6, during B. burgdorferi infection. Using bone marrow-derived macrophages, we found that TRAF6, a known target of miR-146a involved in NF-κB activation, was dysregulated in resting and B. burgdorferi-stimulated B6 miR-146a-/- macrophages, and corresponded to elevated IL-1β, IL-6 and CXCL1 production. This dysregulated protein production was also observed in macrophages treated with IL-10 prior to B. burgdorferi stimulation. Peritoneal macrophages from B6 miR-146a-/- mice also showed enhanced phagocytosis of B. burgdorferi. Together, these data show that miR-146a-mediated regulation of TRAF6 and NF-κB, and downstream targets such as IL-1β, IL-6 and CXCL1, are critical for modulation of Lyme arthritis during chronic infection with B. burgdorferi.

Cerebrospinal fluid T-regulatory cells recognize Borrelia burgdorferi NAPA in chronic Lyme borreliosis

The NapA protein of B. burgdorferi is essential for the persistence of spirochetes in ticks. One of the most intriguing aspects of NapA is its potential to interfere with the host immune system. Here, we investigated the role of the acquired immune responses induced by NapA in the cerebrospinal fluids (CSF) of patients with chronic Lyme borreliosis. We evaluated the cytokine profile induced in microglia cells and CSF T cells following NapA stimulation. We report here that NapA induced a regulatory T (Treg) response in the CSF of patients with chronic Lyme borreliosis and it is able to expand this suppressive response by promoting the production of TGF-beta and IL-10 by microglia cells. Collectively, these data strongly support a central role of NapA in promoting both Treg response and immune suppression in the CSF of patients with chronic Lyme borreliosis and suggest that NapA and the Treg pathway may represent novel therapeutic targets for the prevention and treatment of the disease.

The cytolethal distending toxin of Aggregatibacter actinomycetemcomitans inhibits macrophage phagocytosis and subverts cytokine production

Aggregatibacter actinomycetemcomitans is an important periodontal pathogen that can participate in periodontitis and other non-oral infections. The cytolethal distending toxin (Cdt) is among the virulence factors produced by this bacterium. The Cdt is also secreted by several mucosa-associated Gram-negative pathogens and may play a role in perpetuating the infection by modulating the immune response. Although the toxin targets a wide range of eukaryotic cell types little is known about its activity on macrophages which play a key part in alerting the rest of the immune system to the presence of pathogens and their virulence factors. In view of this, we tested the hypothesis that the A. actinomycetemcomitans Cdt (AaCdt) disrupts macrophage function by inhibiting phagocytic activity as well as affecting the production of cytokines. Murine macrophages were co-cultured with either wild-type A. actinomycetemcomitans or a Cdt(-) mutant. Viable counts and qPCR showed that phagocytosis of the wild-type strain was significantly reduced relative to that of the Cdt(-) mutant. Addition of recombinant Aa(r)Cdt to co-cultures along with the Cdt(-) mutant diminished the phagocytic activity similar to that observed with the wild type strain. High concentrations of Aa(r)Cdt resulted in decreased phagocytosis of fluorescent bioparticles. Nitric oxide production was modulated by the presence of Cdt and the levels of IL-1β, IL-12 and IL-10 were increased. Production of TNF-α did not differ in the co-culture assays but was increased by the presence of Aa(r)Cdt. These data suggest that the Cdt may modulate macrophage function in A. actinomycetemcomitans infected sites by impairing phagocytosis and modifying the pro-inflammatory/anti-inflammatory cytokine balance.

Borrelia burgdorferi elicited-IL-10 suppresses the production of inflammatory mediators, phagocytosis, and expression of co-stimulatory receptors by murine macrophages and/or dendritic cells

Borrelia burgdorferi (Bb) is a tick-borne spirochete that is the causative agent for Lyme disease. Our previous studies indicate that virulent Bb can potently enhance IL-10 production by macrophages (MØs) and that blocking IL-10 production significantly enhances bacterial clearance. We hypothesize that skin-associated APC types, such as MØs and dendritic cells (DCs) are potent producers of IL-10 in response to Bb, which may act in autocrine fashion to suppress APC responses critical for efficient Bb clearance. Our goal is to delineate which APC immune functions are dysregulated by Bb-elicited IL-10 using a murine model of Lyme disease. Our in vitro studies indicated that both APCs rapidly produce IL-10 upon exposure to Bb, that these levels inversely correlate with the production of many Lyme-relevant proinflammatory cytokines and chemokines, and that APCs derived from IL-10(-/-) mice produced greater amounts of these proinflammatory mediators than wild-type APCs. Phagocytosis assays determined that Bb-elicited IL-10 levels can diminish Bb uptake and trafficking by MØs, suppresses ROS production, but does not affect NO production; Bb-elicited IL-10 had little effect on phagocytosis, ROS, and NO production by DCs. In general, Bb exposure caused little-to-no upregulation of several critical surface co-stimulatory markers by MØs and DCs, however eliminating Bb-elicited IL-10 allowed a significant upregulation in many of these co-stimulatory receptors. These data indicate that IL-10 elicited from Bb-stimulated MØs and DCs results in decreased production of proinflammatory mediators and co-stimulatory molecules, and suppress phagocytosis-associated events that are important for mediating both innate and adaptive immune responses by APCs.

Interleukin-10 (IL-10) inhibits Borrelia burgdorferi-induced IL-17 production and attenuates IL-17-mediated Lyme arthritis

Previous studies have shown that cells and cytokines associated with interleukin-17 (IL-17)-driven inflammation are involved in the arthritic response to Borrelia burgdorferi infection. Here, we report that IL-17 is a contributing factor in the development of Lyme arthritis and show that its production and histopathological effects are regulated by interleukin-10 (IL-10). Spleen cells obtained from B. burgdorferi-infected, "arthritis-resistant" wild-type C57BL/6 mice produced low levels of IL-17 following stimulation with the spirochete. In contrast, spleen cells obtained from infected, IL-10-deficient C57BL/6 mice produced a significant amount of IL-17 following stimulation with B. burgdorferi. These mice developed significant arthritis, including erosion of the bones in the ankle joints. We further show that treatment with antibody to IL-17 partially inhibited the significant hind paw swelling and histopathological changes observed in B. burgdorferi-infected, IL-10-deficient mice. Taken together, these findings provide additional evidence of a role for IL-17 in Lyme arthritis and reveal an additional regulatory target of IL-10 following borrelial infection.

Characterizing the syphilis epidemic among men who have sex with men in Lima, Peru to identify new treatment and control strategies

BACKGROUND

Syphilis is an important sexually transmitted infection (STI) with serious public health consequences. Among men who have sex with men (MSM) in Lima, the prevalence and incidence are extraordinarily high. Current syndromic approaches, however, fail to identify asymptomatic cases, and in settings where large proportions of individuals test positive again after treatment, it is frequently difficult to distinguish treatment failure from re-infection. Thus, new approaches are needed to improve treatment strategies and public health control efforts.

METHODS/DESIGN

Study participants will undergo baseline testing for syphilis infection along with a behavioral survey covering demographics, sexual behavior, drug and alcohol abuse and health-care seeking behavior. The cohort will be followed for 18 months at three-month intervals. Blood and earlobe scrapings will also be collected for T. pallidum DNA testing, to create molecular markers for subtyping. We will also perform cytokine testing on collected samples in order to create host immunologic profiles associated with recurrence, re-infection, treatment failure and success.

DISCUSSION

Advances in social epidemiology, molecular typing and characterization of host immune responses will offer promise in developing new understandings of syphilis management. We will share our findings with the Peruvian Ministry of Health and other public health organizations, to identify new approaches of case detection and successful treatment.

Assessment of transcriptional activity of Borrelia burgdorferi and host cytokine genes during early and late infection in a mouse model

Differential gene expression by Borrelia burgdorferi spirochetes during mammalian infection facilitates their dissemination as well as immune evasion. Modulation of gene transcription in response to host immunity has been documented with the outer surface protein C, but the influence of transcription of other genes is largely unknown. A low-density array (LDA) was developed to study transcriptional activity of 43 B. burgdorferi genes and 19 host genes that may be involved in various host-agent interactions. Gene transcription in heart, joint, and muscle tissue was compared in immunocompetent C3H and immunodeficient C3H-scid mice during early (3 weeks) and late (2 months) B. burgdorferi infection. Among all tissue types, levels of relative transcription of over 80% of B. burgdorferi genes tested were one- to nine-fold less in C3H mice compared to C3H-scid mice. At the later time point, all genes were transcribed in C3H-scid mice, whereas transcription of 16 genes out of 43 tested was not detected in analyzed tissues of C3H mice. Our data suggest that during infection of immunocompetent mice, a majority of B. burgdorferi genes tested are downregulated in response to acquired host immunity. LDA revealed variable patterns of host gene expression in different tissues and at different intervals in infected mice. Higher levels of relative expression for IL-10 during both early and late infection were detected in heart base, and it was unchanged in the tibiotarsal joint. Comparative analysis of B. burgdorferi and host genes transcriptional activity revealed that increased flaB mRNA during early infection was followed by increases of CCL7, CCL8, interleukin-10 (IL-10), and tumor necrosis factor-α (TNF-α) in all assessed tissue types. LDA represents a valuable approach for sensitive and quantitative gene transcription profiling and for understanding Lyme borreliosis.

Different patterns of expression and of IL-10 modulation of inflammatory mediators from macrophages of Lyme disease-resistant and -susceptible mice

C57BL/6J (C57) mice develop mild arthritis (Lyme disease-resistant) whereas C3H/HeN (C3H) mice develop severe arthritis (Lyme disease-susceptible) after infection with the spirochete Borrelia burgdorferi. We hypothesized that susceptibility and resistance to Lyme disease, as modeled in mice, is associated with early induction and regulation of inflammatory mediators by innate immune cells after their exposure to live B. burgdorferi spirochetes. Here, we employed multiplex ELISA and qRT-PCR to investigate quantitative differences in the levels of cytokines and chemokines produced by bone marrow-derived macrophages from C57 and C3H mice after these cells were exposed ex vivo to live spirochetes or spirochetal lipoprotein. Upon stimulation, the production of both cytokines and chemokines was up-regulated in macrophages from both mouse strains. Interestingly, however, our results uncovered two distinct patterns of spirochete- and lipoprotein-inducible inflammatory mediators displayed by mouse macrophages, such that the magnitude of the chemokine up-regulation was larger in C57 cells than it was in C3H cells, for most chemokines. Conversely, cytokine up-regulation was more intense in C3H cells. Gene transcript analyses showed that the displayed patterns of inflammatory mediators were associated with a TLR2/TLR1 transcript imbalance: C3H macrophages expressed higher TLR2 transcript levels as compared to those expressed by C57 macrophages. Exogenous IL-10 dampened production of inflammatory mediators, especially those elicited by lipoprotein stimulation. Neutralization of endogenously produced IL-10 increased production of inflammatory mediators, notably by macrophages of C57 mice, which also displayed more IL-10 than C3H macrophages. The distinct patterns of pro-inflammatory mediator production, along with TLR2/TLR1 expression, and regulation in macrophages from Lyme disease-resistant and -susceptible mice suggests itself as a blueprint to further investigate differential pathogenesis of Lyme disease.

Localized production of IL-10 suppresses early inflammatory cell infiltration and subsequent development of IFN-γ-mediated Lyme arthritis

IL-10 is a nonredundant inflammatory modulator that suppresses arthritis development in Borrelia burgdorferi-infected mice. Infected C57BL/6 (B6) IL-10(-/-) mice were previously found to have a prolonged IFN-inducible response in joint tissue. Infection of B6 IL-10 reporter mice identified macrophages and CD4(+) T cells as the primary sources of IL-10 in the infected joint tissue, suggesting that early local production of IL-10 dampened the proarthritic IFN response. Treatment of B6 IL-10(-/-) mice with anti-IFN-γ reduced the increase in arthritis severity and suppressed IFN-inducible transcripts to wild-type levels, thereby linking dysregulation of IFN-γ to disease in the B6 IL-10(-/-) mouse. Arthritis in B6 IL-10(-/-) mice was associated with elevated numbers of NK cell, NKT cell, α/β T cell, and macrophage infiltration of the infected joint. FACS lineage sorting revealed NK cells and CD4(+) T cells as sources of IFN-γ in the joint tissue of B6 IL-10(-/-) mice. These findings suggest the presence of a positive-feedback loop in the joint tissue of infected B6 IL-10(-/-) mice, in which production of inflammatory chemokines, infiltration of IFN-γ-producing cells, and additional production of inflammatory cytokines result in arthritis. This mechanism of arthritis is in contrast to that seen in C3H/He mice, in which arthritis development is linked to transient production of type I IFN and develops independently of IFN-γ. Due to the sustained IFN response driven by NK cells and T cells, we propose the B6 IL-10(-/-) mouse as a potential model to study the persistent arthritis observed in some human Lyme disease patients.

ELISA-based measurement of antibody responses and PCR-based detection profiles can distinguish between active infection and early clearance of Borrelia burgdorferi

Borrelia burgdorferi is a spirochetal bacterium that causes Lyme disease. These studies address whether current research methods using either ELISA to detect seroconversion to B. burgdorferi antigens or PCR quantification of bacterial DNA within tissues can accurately distinguish between a productive infection versus a B. burgdorferi exposure that is rapidly cleared by the innate responses. Mice receiving even minimal doses of live B. burgdorferi produced significantly more B. burgdorferi-specific IgM and IgG than groups receiving large inocula of heat-killed bacteria. Additionally, sera from mice injected with varied doses of killed B. burgdorferi recognized unique borrelial antigens compared to mice infected with live B. burgdorferi. Intradermal injection of killed B. burgdorferi resulted in rapid DNA clearance from skin, whereas DNA was consistently detected in skin inoculated with viable B. burgdorferi. These data indicate that both ELISA-based serological analyses and PCR-based methods of assessing B. burgdorferi infection clearly distinguish between an established infection with live bacteria and exposure to large numbers of bacteria that are promptly cleared by the innate responses.

Interleukin-10 alters effector functions of multiple genes induced by Borrelia burgdorferi in macrophages to regulate Lyme disease inflammation

Interleukin-10 (IL-10) modulates inflammatory responses elicited in vitro and in vivo by Borrelia burgdorferi, the Lyme disease spirochete. How IL-10 modulates these inflammatory responses still remains elusive. We hypothesize that IL-10 inhibits effector functions of multiple genes induced by B. burgdorferi in macrophages to control concomitantly elicited inflammation. Because macrophages are essential in the initiation of inflammation, we used mouse J774 macrophages and live B. burgdorferi spirochetes as the model target cell and stimulant, respectively. First, we employed transcriptome profiling to identify genes that were induced by stimulation of cells with live spirochetes and that were perturbed by addition of IL-10 to spirochete cultures. Spirochetes significantly induced upregulation of 347 genes at both the 4-h and 24-h time points. IL-10 inhibited the expression levels, respectively, of 53 and 65 of the 4-h and 24-h genes, and potentiated, respectively, at 4 h and 24 h, 65 and 50 genes. Prominent among the novel identified IL-10-inhibited genes also validated by quantitative real-time PCR (qRT-PCR) were Toll-like receptor 1 (TLR1), TLR2, IRAK3, TRAF1, IRG1, PTGS2, MMP9, IFI44, IFIT1, and CD40. Proteome analysis using a multiplex enzyme-linked immunosorbent assay (ELISA) revealed the IL-10 modulation/and or potentiation of RANTES/CCL5, macrophage inflammatory protein 2 (MIP-2)/CXCL2, IP-10/CXCL10, MIP-1α/CCL3, granulocyte colony-stimulating factor (G-CSF)/CSF3, CXCL1, CXCL5, CCL2, CCL4, IL-6, tumor necrosis factor alpha (TNF-α), IL-1α, IL-1β, gamma interferon (IFN-γ), and IL-9. Similar results were obtained using sonicated spirochetes or lipoprotein as stimulants. Our data show that IL-10 alters effectors induced by B. burgdorferi in macrophages to control concomitantly elicited inflammatory responses. Moreover, for the first time, this study provides global insight into potential mechanisms used by IL-10 to control Lyme disease inflammation.

Impairment of survival signaling and efferocytosis in TRPC3-deficient macrophages

We have recently shown that in macrophages proper operation of the survival pathways phosphatidylinositol-3-kinase (PI3K)/AKT and nuclear factor kappa B (NFkB) has an obligatory requirement for constitutive, non-regulated Ca(2+) influx. In the present work we examined if Transient Receptor Potential Canonical 3 (TRPC3), a member of the TRPC family of Ca(2+)-permeable cation channels, contributes to the constitutive Ca(2+) influx that supports macrophage survival. We used bone marrow-derived macrophages obtained from TRPC3(-/-) mice to determine the activation status of survival signaling pathways, apoptosis and their efferocytic properties. Treatment of TRPC3(+/+) macrophages with the pro-apoptotic cytokine TNFα induced time-dependent phosphorylation of IκBα, AKT and BAD, and this was drastically reduced in TRPC3(-/-) macrophages. Compared to TRPC3(+/+) cells TRPC3(-/-) macrophages exhibited reduced constitutive cation influx, increased apoptosis and impaired efferocytosis. The present findings suggest that macrophage TRPC3, presumably through its constitutive function, contributes to survival signaling and efferocytic properties.

Neuroborreliosis: pathogenesis, symptoms, diagnosis and treatment

Lyme disease is the most common human tick-borne disease in the northern hemisphere. This article describes the current knowledge of several aspects of Lyme neuroborreliosis. The epidemiology is reviewed first, with special respect to the difference between European and American disease. Then, the current knowledge about the pathogenesis of Lyme neuroborreliosis is presented, with emphasis on immune evasion strategies. Furthermore, the clinical picture of acute Lyme neuroborreliosis and the frequently discussed post-Lyme disease syndrome are critically discussed. The commonly used diagnostic strategies, as well as the relevance of the lymphocyte transformation test, CD57+/CD3- cell count and CXCL13, are presented. Finally, the therapeutic options are described to give a balanced overview of all aspects of this disease.

Nod2 suppresses Borrelia burgdorferi mediated murine Lyme arthritis and carditis through the induction of tolerance

The internalization of Borrelia burgdorferi, the causative agent of Lyme disease, by phagocytes is essential for an effective activation of the immune response to this pathogen. The intracellular, cytosolic receptor Nod2 has been shown to play varying roles in either enhancing or attenuating inflammation in response to different infectious agents. We examined the role of Nod2 in responses to B. burgdorferi. In vitro stimulation of Nod2 deficient bone marrow derived macrophages (BMDM) resulted in decreased induction of multiple cytokines, interferons and interferon regulated genes compared with wild-type cells. However, B. burgdorferi infection of Nod2 deficient mice resulted in increased rather than decreased arthritis and carditis compared to control mice. We explored multiple potential mechanisms for the paradoxical response in in vivo versus in vitro systems and found that prolonged stimulation with a Nod2 ligand, muramyl dipeptide (MDP), resulted in tolerance to stimulation by B. burgdorferi. This tolerance was lost with stimulation of Nod2 deficient cells that cannot respond to MDP. Cytokine patterns in the tolerance model closely paralleled cytokine profiles in infected Nod2 deficient mice. We propose a model where Nod2 has an enhancing role in activating inflammation in early infection, but moderates inflammation after prolonged exposure to the organism through induction of tolerance.

Emergence of chronic Lyme arthritis: putting the breaks on CD28 costimulation

Lyme disease is a debilitating infection that is caused upon a bite of Borrelia burgdorferi (Bb)-infected ticks. One of the most prominent clinical manifestations is the development of chronic Lyme arthritis. Months after Bb infection, approximately 60% of untreated Lyme patients experience intermittent arthritic attacks that may last for years. The use of the CD28(-/-) mouse in Bb infection has helped to shed light into the mechanisms that govern this inflammatory process, which seems to be tightly regulated. In this current review, the effect of immunoregulation, as well as CD28 deficiency in the development of chronic Lyme arthritis is discussed.

Identification of Burkholderia mallei and Burkholderia pseudomallei adhesins for human respiratory epithelial cells

Background

Burkholderia pseudomallei and Burkholderia mallei cause the diseases melioidosis and glanders, respectively. A well-studied aspect of pathogenesis by these closely-related bacteria is their ability to invade and multiply within eukaryotic cells. In contrast, the means by which B. pseudomallei and B. mallei adhere to cells are poorly defined. The purpose of this study was to identify adherence factors expressed by these organisms.

Results

Comparative sequence analyses identified a gene product in the published genome of B. mallei strain ATCC23344 (locus # BMAA0649) that resembles the well-characterized Yersinia enterocolitica autotransporter adhesin YadA. The gene encoding this B. mallei protein, designated boaA, was expressed in Escherichia coli and shown to significantly increase adherence to human epithelial cell lines, specifically HEp2 (laryngeal cells) and A549 (type II pneumocytes), as well as to cultures of normal human bronchial epithelium (NHBE). Consistent with these findings, disruption of the boaA gene in B. mallei ATCC23344 reduced adherence to all three cell types by ~50%. The genomes of the B. pseudomallei strains K96243 and DD503 were also found to contain boaA and inactivation of the gene in DD503 considerably decreased binding to monolayers of HEp2 and A549 cells and to NHBE cultures.

A second YadA-like gene product highly similar to BoaA (65% identity) was identified in the published genomic sequence of B. pseudomallei strain K96243 (locus # BPSL1705). The gene specifying this protein, termed boaB, appears to be B. pseudomallei-specific. Quantitative attachment assays demonstrated that recombinant E. coli expressing BoaB displayed greater binding to A549 pneumocytes, HEp2 cells and NHBE cultures. Moreover, a boaB mutant of B. pseudomallei DD503 showed decreased adherence to these respiratory cells. Additionally, a B. pseudomallei strain lacking expression of both boaA and boaB was impaired in its ability to thrive inside J774A.1 murine macrophages, suggesting a possible role for these proteins in survival within professional phagocytic cells.

Conclusions

The boaA and boaB genes specify adhesins that mediate adherence to epithelial cells of the human respiratory tract. The boaA gene product is shared by B. pseudomallei and B. mallei whereas BoaB appears to be a B. pseudomallei-specific adherence factor.

Interleukin-10 mediated autoregulation of murine B-1 B-cells and its role in Borrelia hermsii infection

B cells are typically characterized as positive regulators of the immune response, primarily by producing antibodies. However, recent studies indicate that various subsets of B cells can perform regulatory functions mainly through IL-10 secretion. Here we discovered that peritoneal B-1 (B-1P) cells produce high levels of IL-10 upon stimulation with several Toll-like receptor (TLR) ligands. High levels of IL-10 suppressed B-1P cell proliferation and differentiation response to all TLR ligands studied in an autocrine manner in vitro and in vivo. IL-10 that accumulated in cultures inhibited B-1P cells at second and subsequent cell divisions mainly at the G1/S interphase. IL-10 inhibits TLR induced B-1P cell activation by blocking the classical NF-κB pathway. Co-stimulation with CD40 or BAFF abrogated the IL-10 inhibitory effect on B-1P cells during TLR stimulation. Finally, B-1P cells adoptively transferred from the peritoneal cavity of IL-10^−/− mice showed better clearance of Borrelia hermsii than wild-type B-1P cells. This study described a novel autoregulatory property of B-1P cells mediated by B-1P cell derived IL-10, which may affect the function of B-1P cells in infection and autoimmunity.

Cytokine expression during syphilis infection in HIV-1-infected individuals

BACKGROUND

Little is known about cytokine responses to syphilis infection in HIV-1-infected individuals.

METHODS

We retrospectively identified patients with HIV-1 and Treponema pallidum coinfection. Plasma samples from before, during, and after coinfection were analyzed for interleukin (IL)-2, IL-4, IL-6, IL-8, IL-10, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha.

RESULTS

Thirty-six patients were included. IL-10 levels increased significantly in patients with primary or secondary stage syphilis from a median of 12.8 pg/mL [interquartile range (IQR), 11.0-27.8] before infection to 46.7 pg/mL (IQR, 28.4-78.9) at the time of diagnosis (P = 0.027) and decreased to 13.0 pg/mL (IQR, 6.2-19.4) after treatment of syphilis (P <0.001). TNF-alpha levels showed no significant change from before to during syphilis in patients with primary or secondary stage syphilis (median 3.9 pg/mL (IQR, 3.3-9.6) and 9.0 pg/mL (IQR, 5.4-12.6), respectively (P = 0.31); however, treatment of syphilis was associated with a significant decrease in TNF-alpha to a median of 4.2 pg/mL (IQR, 2.7-6.8) (P <0.001). No significant changes in cytokine levels were observed in coinfected with latent stage syphilis.IL-10 and TNF-alpha levels correlated positively with plasma HIV RNA values at the time of diagnosis (r = 0.38, P = 0.023, and r = 0.64, P <0.001, respectively) and correlated inversely with CD4 T cell counts (-0.35, P = 0.036 and r = -0.34, P = 0.042, respectively).

CONCLUSION

HIV-1 and early stage syphilis coinfection were associated with an increase in IL-10. IL-10 and TNF-alpha both decreased after treatment of syphilis. TNF-alpha and IL-10 correlated with low CD4 T cell counts and high plasma HIV RNA values.

Regulation of T-helper-cell lineage development by osteopontin: the inside story

Studies of osteopontin (OPN)-dependent regulation of immune responses have focused on the cytokine activities of the secreted form of this protein. Recent evidence has revealed that an intracellular form of OPN expressed by dendritic cells regulates the expression of pro-inflammatory cytokines and the differentiation of T helper (T(H))-cell lineages. In this Opinion article, we discuss the properties of both OPN isoforms and their respective contributions to the immune response. We propose that cell-type-specific expression of secreted and intracellular OPN regulates the development of distinct effector T(H) cells, including that of T(H)1 and T(H)17 cells.

Effect of IL-10 on neutrophil recruitment and survival after Pseudomonas aeruginosa challenge

IL-10 is a potent, endogenous anti-inflammatory cytokine known to decrease cytokine and keratinocyte-derived chemokine (KC) expression. Traditionally, in vivo effects of IL-10 were extrapolated from studies employing systemic antibody neutralization. As a result, divergent data regarding the protective and/or harmful roles of IL-10 have been reported. In this study, we used a lung-specific, tetracycline-inducible IL-10 overexpression-transgenic (IL-10 OE) mouse to study the effects of IL-10 overexpression on Pseudomonas aeruginosa-induced lung inflammation and corresponding survival in mice. Overexpression of IL-10 in the lung significantly increased mortality. During the early phase after infection (6-hours after infection), neutrophil recruitment as well as cytokine (TNF-alpha) and chemokine (KC) expression were significantly decreased in the IL-10 OE mice, which resulted in attenuated bacterial clearance. In contrast, overzealous production of KC and TNF-alpha intensified neutrophil infiltration and increased vascular leakage in IL-10 OE mice at the later stage of infection (24 hours after infection). Neutrophil depletion showed impaired bacterial clearance in both control and IL-10 OE mice, and further enhanced mouse mortality, whereas exogenous administration of KC reversed this finding. Our data indicate that early neutrophil recruitment is important for combating bacterial infection, and that the inhibition of neutrophil recruitment by IL-10 results in insufficient bacteria clearance in the lung, leading to excessive development of inflammation and increased mortality.

Adenoviral delivery of interleukin-10 fails to attenuate experimental Lyme disease

Production of interleukin-10 (IL-10) by C57BL/6 mice following infection with Borrelia burgdorferi has been proposed as a mechanism whereby resistance to the development of experimental Lyme arthritis is maintained. In the current study, we sought to determine the role of IL-10 during infection of arthritis- and carditis-susceptible C3H mice. Infection of C3H IL-10(-/-) mice led to increased joint swelling and arthritis severity scores over those of wild-type C3H mice. Measurement of B. burgdorferi numbers in joints or disseminated tissues indicated a more efficient clearance of spirochetes in the absence of IL-10, similar to that reported in C57BL/6 IL-10(-/-) mice. However, in contrast to previous in vitro work, infection of C3H IL-10(-/-) mice led to decreased in vivo expression of the cytokines KC, IL-1beta, IL-4, and IL-12p70 in the infected joints. Finally, adenoviral expression of IL-10 in the infected joints of C3H mice was unable to modulate the development of severe Lyme arthritis and had no effect on spirochete clearance or Borrelia-specific antibody production. Development of Lyme carditis appeared to be independent of modulation by IL-10. These results suggest that IL-10 limits the development of joint inflammation in both arthritis-resistant and -susceptible mouse strains infected with B. burgdorferi and that increased IL-10 production cannot rescue genetic susceptibility to development of pathology in this model.

Relapsing fever borreliosis in interleukin-10-deficient mice

Relapsing fever (RF) is a spirochetal infection characterized by periods of sickness with fever at time of high bacteremia that alternate with afebrile periods of relative well being during low bacteremia. Patients with epidemic RF who are doing relatively well have extraordinarily high levels of interleukin-10 (IL-10) in the circulation. We investigated the possibility that IL-10 plays an important protective role in this infection using wild-type and IL-10-deficient mice inoculated with virulent serotype 2 of the RF spirochete Borrelia turicatae. During peak bacteremia there was increased systemic production of IL-10 that quickly resolved in the postpeak period; in contrast, IL-6 and CXCL13 production increased during the peak but remained elevated during postpeak bacteremia. IL-10 deficiency resulted in lower bacteremia, increased specific antibody production, higher production of CXCL13 and IL-6, and thrombotic and hemorrhagic complications affecting multiple organs with secondary tissue injury. Our results revealed that production of IL-10 is highly regulated during RF and plays an important protective role in the prevention of hemorrhagic and thrombotic complications at the cost of reduced pathogen control.

IL-10 helps control pathogen load during high-level bacteremia

During relapsing fever borreliosis, a high pathogen load in the blood occurs at times of peak bacteremia. Specific IgM Abs are responsible for spirochetal clearance so in absence of B cells there is persistent high-level bacteremia. Previously, we showed that B cell-deficient mice persistently infected with Borrelia turicatae produce high levels of IL-10 and that exogenous IL-10 reduces bacteremia. This suggested that IL-10 helps reduce bacteremia at times of high pathogen load by a B cell-independent mechanism, most likely involving innate immunity. To investigate this possibility, we compared B. turicatae infection in RAG2/IL-10(-/-) and RAG2(-/-) mice. The results showed that IL-10 deficiency resulted in significantly higher bacteremia, higher TNF levels, and early mortality. Examination of the spleen and peripheral blood showed markedly increased apoptosis of immune cells in infected RAG2/IL-10(-/-) mice. Neutralization of TNF reduced apoptosis of leukocytes and splenocytes, increased production of IFN-gamma by NK cells, increased phagocytosis in the spleen, decreased spirochetemia, and rescued mice from early death. Our results indicate that at times of high pathogen load, as during peak bacteremia in relapsing fever borreliosis, IL-10 protects innate immune cells from apoptosis via inhibition of TNF resulting in improved pathogen control.

The pathogenesis of lyme neuroborreliosis: from infection to inflammation

This review describes the current knowledge of the pathogenesis of acute Lyme neuroborreliosis (LNB), from invasion to inflammation of the central nervous system. Borrelia burgdorferi (B.b.) enters the host through a tick bite on the skin and may disseminate from there to secondary organs, including the central nervous system. To achieve this, B.b. first has to evade the hostile immune system. In a second step, the borrelia have to reach the central nervous system and cross the blood-brain barrier. Once in the cerebrospinal fluid (CSF), the spirochetes elicit an inflammatory response. We describe current knowledge about the infiltration of leukocytes into the CSF in LNB. In the final section, we discuss the mechanisms by which the spirochetal infection leads to the observed neural dysfunction. To conclude, we construct a stringent concept of the pathogenesis of LNB.

Gene expression profiling provides insights into the pathways involved in inflammatory arthritis development: murine model of Lyme disease

The spirochete Borrelia burgdorferi, the etiologic agent of Lyme disease, causes severe subacute arthritis in susceptible inbred mouse strains, such as C3H/HeN, but only mild arthritis in resistant strains such as C57BL/6. The degree of Lyme arthritis severity is controlled in part by host genetics and several quantitative trait loci have been identified which contribute to this regulation. In addition, the anti-inflammatory cytokine IL-10 assumes an important role in the control of arthritis in C57BL/6 mice. However, the identification of genes and signaling pathways that dictate arthritis severity has remained elusive. In an attempt to elucidate such genes and pathways, the power of microarray analysis was combined with information gleaned from gene manipulation models. As a result of this approach, two novel gene profiles were identified: an IFN-inducible profile in arthritis-susceptible C3H and IL-10(-/-) mice, and an epidermal/differentiation profile in C57BL/6 mice. Application of this information to TLR2(-/-) mice, which also develop severe arthritis, indicated that they also upregulated IFN-responsive genes. These results provided new insight into the regulation of Lyme arthritis development and illustrated the utility of combining gene expression analyses with genetically manipulated mouse models in unraveling mechanisms underlying specific disease processes.

Review: variability of host-pathogen interaction

The course of every infection is different. The same pathogen can lead to subclinical, mild, severe or lethal infections in individuals. But is this just chance or determined by individual differences--on the side of the host as well as on the side of the pathogen? If so, we might need to consider these variations for treatment decisions. Indeed, we now understand that genetic polymorphisms and health status represent inborn and acquired risk factors. Similarly, pathogens impress with an increasing number of already identified virulence factors and host response modifiers. The emerging, more complex, view of the factors determining course and outcome of infections promises to enable more tailored and thus, hopefully, more effective treatment decisions.

CD28 deficiency exacerbates joint inflammation upon Borrelia burgdorferi infection, resulting in the development of chronic Lyme arthritis

Lyme disease, caused by the tick-borne spirochete Borrelia burgdorferi (Bb), is a multisystem illness, affecting many organs, such as the heart, the nervous system, and the joints. Months after Bb infection, approximately 60% of patients experience intermittent arthritic attacks, a condition that in some individuals progresses to chronic joint inflammation. Although mice develop acute arthritis in response to Bb infection, the joint inflammation clears after 2 wk, despite continuous infection, only very rarely presenting with chronic Lyme arthritis. Thus, the lack of an animal system has so far prevented the elucidation of this persistent inflammatory process that occurs in humans. In this study, we report that the majority of Bb-infected CD28-/- mice develop chronic Lyme arthritis. Consistent with observations in chronic Lyme arthritis patients, the infected mutant, but not wild-type mice present recurring monoarticular arthritis over an extended time period, as well as anti-outer surface protein A of Bb serum titers. Furthermore, we demonstrate that anti-outer surface protein A Abs develop in these mice only after establishment of chronic Lyme arthritis. Thus, the Bb-infected CD28-/- mice provide a murine model for studying chronic Lyme arthritis.